Solid state laser with dual cooling loops

Abstract

An optically-pumped solid state laser system having separate subsystems for cooling its gain medium and optical pumping assembly. The invention permits the operating temperatures of the gain medium and optical pumping assembly to be independently controlled, and permits a substantial increase in cooling efficiency as a result of independent control of coolant flow rates in the two cooling subsystems. In a class of preferred embodiments, the gain medium cooling subsystem includes a first channel through which coolant flows with relatively high flow rate and relatively low temperature (to maintain the gain medium at a desired low operating temperature), and the other cooling subsystem includes a second channel through which coolant flows with a relatively low flow rate and relatively high temperature. In one embodiment, the gain medium is a Holmium:YAG rod, and a Cerium doped glass tube surrounds the rod. Three to four gallons per minute of coolant flows through the tube to maintain the rod at an operating temperature in the range from about + 10 to - 15 degrees Celsius. The optical pumping assembly includes a set of flash lamps, and a Cerium doped glass tube surrounds each lamp. A total of no more than two gallons per minute of coolant flows through the tubes around the lamps, to maintain the lamps at a relatively high (but controlled) temperature.

What is claimed is: 
     
       1. A solid state laser system, including: a gain medium;   an optical pumping means spatially separated from the gain medium;   the first coolant flow channel surrounding the optical pumping means; and   a second coolant flow channel surrounding the gain medium, wherein the optical pumping means includes at least one flash lamp which emits pumping radiation, the first coolant flow channel includes a first tube which is transmissive to the pumping radiation and includes a first coolant gas flowing therethrough, and the second coolant flow channel includes a second tube which is transmissive to the pumping radiation and includes a second coolant fluid flowing therethrough, wherein the second coolant fluid is a liquid mixture of water and alcohol.   
     
     
       2. The system of claim 1, wherein the gain medium is rod-shaped, the optical pumping means comprises at least one flash lamp which emits pumping radiation, the first coolant flow channel includes a first tube transmissive to the pumping radiation, and the second coolant flow channel includes a second tube transmissive to the pumping radiation. 
     
     
       3. The system of claim 2, wherein the first tube and the second tube are composed of Cerium doped glass. 
     
     
       4. The system of claim 1, wherein the gain medium is a rod composed of Holmium:YAG material. 
     
     
       5. The system of claim 1, wherein the gain medium is a rod composed of Holmium:YLF material. 
     
     
       6. The system of claim 1, wherein the gain medium is a Holmium-doped rod, the first coolant gas has a temperature and flow rate sufficient to maintain the optical pumping means at a first temperature, and the second coolant fluid has a temperature and flow rate sufficient to maintain the rod at a second temperature lower than the first temperature during lasing operation. 
     
     
       7. The system of claim 6, wherein the Holmium-doped rod is composed of Holmium-YAG material. 
     
     
       8. The system of claim 6, wherein the second temperature is in the range from +10 degrees Celsius to -15 degrees Celsius. 
     
     
       9. The system of claim 8, wherein the first coolant gas is Xenon gas having a first flow rate, and the second coolant fluid has a second flow rate substantially greater than the first flow rate. 
     
     
       10. The system of claim 9, wherein the first flow rate is not greater than two gallons per minute, and the second flow rate is in the range from three to four gallons per minute. 
     
     
       11. The system of claim 6, wherein the first coolant gas is Xenon gas. 
     
     
       12. The system of claim 1, wherein the first coolant gas maintains the optical pumping means at a first temperature, and the second coolant fluid maintains the gain medium at a second temperature lower than the first temperature during lasing operation. 
     
     
       13. A cooling system for a laser including a solid state gain medium and an optical pumping means spatially separated from said gain medium, said cooling system including: a first coolant flow channel surrounding the optical pumping means;   a second coolant flow channel surrounding the gain medium;   first coolant means for pumping a first coolant gas having a first flow rate and a first temperature into the first coolant flow channel; and   second coolant means for pumping a second coolant fluid having a second flow rate and a second temperature into the second coolant flow channel, wherein the second coolant fluid is a liquid mixture of water and alcohol.   
     
     
       14. The system of claim 13, wherein the first coolant flow channel includes a first glass tube, the second coolant flow channel includes a second glass tube, the first coolant means includes a first hose connected to an inlet end of the first glass tube, and the second coolant means includes a second hose connected to an inlet end of the second glass tube. 
     
     
       15. The system of claim 14, wherein the gain medium is a rod composed of Holmium:YAG material, the optical pumping means includes at least one flash lamp which emits pumping radiation, and the first glass tube and the second glass tube are transmissive to the pumping radiation, and the second temperature and the second flow rate are sufficient to maintain the rod at an operating temperature substantially lower than the first temperature during lasing operation. 
     
     
       16. The system of claim 15, wherein the operating temperature is in the range from +10 degrees Celsius to -15 degrees Celsius. 
     
     
       17. The system of claim 13, wherein the first coolant gas is Xenon gas, and the second flow rate is substantially greater than the first flow rate. 
     
     
       18. The system of claim 19, wherein the first flow rate is not greater than two gallons per minute, and the second flow rate is in the range from three to four gallons per minute.